Finds a perpendicular vector

Finds a perpendicular vector of input (3-dim)

This simple function finds one of the infinitely many perpendicular vectors of the input vector limited for 3 dimensions.
I use this in my master thesis to find one of the two vectors that span a plane (where the input is the normal vector to the plane). The other vector that spans the plane is of course the cross produkt of the normal and the first perpendicular vector.